Mates connect parts in an assembly and define how they can move relative to each other. This is the most common place students get stuck in Onshape — parts float everywhere or refuse to move. Click each mate type to understand when to use it.
The mental model: Every part has 6 degrees of freedom (DOF) — 3 translation (X, Y, Z) and 3 rotation (Roll, Pitch, Yaw). A mate removes some of those freedoms. Your goal is to remove exactly the right ones. Too few = part floats. Too many = over-constrained and breaks.
🔗 The 6 Mate Types — Click to Explore
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Fastened
Completely rigid — no movement
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Revolute
Spins around one axis only
↔
Slider
Slides along one axis only
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Planar
Slides on a flat surface
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Cylindrical
Spins AND slides along axis
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Ball
Rotates freely in all directions
🪛 The VRC Shaft Stack — Step by Step
Every drive shaft in VRC uses the same mate pattern: bearing→shaft→gear→spacer→wheel. Here's the exact sequence of mates to apply.
VRC Drive Shaft Stack — Mate Sequence
📹 Official Onshape Training Video
Onshape's "CAD for VEX Using Onshape" Level 4 covers assembly mates specifically for VRC parts. Hosted on the official Onshape YouTube channel.
▶ OFFICIAL ONSHAPE TRAINING — LEVEL 4: CONNECTING PARTS
Most common mistake: Using Fastened where you need Revolute. A gear Fastened to a shaft looks right in the model but won't move in simulation — and more importantly, it implies the gear is welded to the shaft, which means when you physically build it, the gear must be locked to the shaft too. Use Revolute for anything that should spin, Fastened only for things that don't move relative to each other.
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OFFICIAL ONSHAPE DOCUMENTATION
Mate reference, VEX parts library guide, and Learning Center robotics curriculum
⚙ STEM HighlightEngineering: Kinematic Pairs & Degrees of Freedom
Onshape mates are digital models of kinematic pairs — mechanical joints that constrain relative motion between parts. Each mate type removes specific degrees of freedom (DOF): a fastened mate removes all 6 DOF, a revolute mate removes 5 (allowing only rotation), a slider mate removes 5 (allowing only translation). Proper mate application ensures the CAD model moves identically to the physical assembly — essential for motion simulation and interference checking before cutting metal.
🎤 Interview line: “We use mates deliberately to simulate mechanism motion in CAD before building. Our four-bar linkage was validated in Onshape — we applied revolute mates at all four pivots and used motion simulation to confirm the arm path cleared the robot body. This caught an interference at full extension before fabrication, saving a rebuild.”
A revolute mate between two Onshape parts allows which type of relative motion?
⬛ Translation along one axis — the parts can slide relative to each other
⬛ Rotation around one axis only — like a pin joint or hinge
⬛ Full 3D rotation in any direction — like a ball-and-socket joint
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Notebook entry tip:Build & Program — Orange slide — Include a CAD assembly screenshot in your mechanism design entry showing the mates applied to your primary mechanism. Annotate which mate type was used at each joint and what motion it allows. A sentence explaining "we validated this linkage motion in CAD before fabricating" is strong notebook evidence that your team used CAD as an engineering tool, not just for documentation.